Quantitative cross-sectoral impact assessments for differing scenarios are
not yet available for Australia and New Zealand. Regional impacts will vary
nonlinearly with time before and after stabilization of GHG concentrations.
Warming will continue to increase after stabilization, but the beneficial effects
of CO2 on plants will no longer increase. Moreover, regional patterns
of rainfall change, particularly in southern Australian and New Zealand areas,
will tend to reverse after stabilization of GHGs (see Section
12.1.5.1). These complexities, together with the continuing post-stabilization
rise in sea level, mean that estimated impacts at the time of stabilization
may not be sufficient to determine whether the level of stabilization is a safe
one.

12.9.5. Uncertainties and Risk Management

Given that some of the climate sensitivities listed in Section
12.9.6, and especially in Table 12-2, already have
been observed for natural climate variations (such as El Niño), confidence
is high that a range of impacts will occur in Australia and New Zealand as a
result of climate change over the coming decades. This level of certainty, and
the possibility that the early stages of greenhouse-related changes already
may be occurring, justify prudent risk management through initiation of appropriate
mitigation and adaptation strategies. Probabilistic assessments of risk, which
account for the uncertainties, are regarded as a way forward. These assessments
attempt to quantify the various sources of uncertainty to provide a conditional
probability of climate change that would cause critical system performance thresholds
to be exceeded and require adaptation or result in losses. Stakeholders may
define their own subjective levels of acceptable risk and plan accordingly to
adapt before or when the threshold is exceeded. Some examples for Australia
and New Zealand are presented in this chapter (see Sections
12.5.2, 12.6.1, 12.8.2,
and 12.8.4), but more are needed.

12.9.6. Vulnerability and Adaptability in Australia and New Zealand

The key regional concerns identified in this chapter regarding vulnerability
to climate change impacts are ecosystem uniqueness, isolation, and vulnerability;
agricultural commodities and terms of trade; droughts, floods, and water supply;
increased coastal and tropical exposure to climate hazards; impacts on indigenous
peoples and their involvement in adaptation planning; coral reefs; and Australian
alpine areas.

Major expected impacts, vulnerability, and adaptability are summarized in Table
12-2. Note that although Australian and (to a lesser extent) New Zealand
farmers have adapted, at least in part, to existing El Niño-related droughts,
they depend on good years for recovery. Thus, despite their adaptability, they
are quite vulnerable to any increase in the frequency of drought or to a tendency
for droughts to last for a longer period. This vulnerability flows through to
the rural communities that service them (see Section
12.5.6).

Several of these vulnerabilities are likely to interact synergistically with
each other and with other environmental stresses. Moreover, vulnerability is
a result of exposure to hazard and capacity to adapt. Thus, vulnerability will
be greatly affected by future changes in demography, economic and institutional
capacity, technology, and the existence of other stresses.

There have been no rigorous studies for Australia or New Zealand that have
taken all of these variables into account. Thus, Table 12-2 is based largely
on studies that assume that the society that is being impacted is much like
that of today. It should not be assumed, however, that socioeconomic changes
in the future necessarily will reduce vulnerability in Australia and New Zealand.
Indeed, many existing socioeconomic trends may exacerbate the problems. For
instance, the bias toward population and economic growth in coastal areas, especially
in the tropics and subtropics, by itself will increase exposure to sea-level
rise and more intense tropical cyclones. If such trends are not to increase
vulnerability, they will need to be accompanied by a conscious process of planning
to reduce vulnerability by other means (e.g., changes in zoning and engineering
design criteria). Thus, vulnerability estimates are based on present knowledge
and assumptions and can be changed by new developments, including planned adaptation.

Table 12-2: Main areas of vulnerability and adaptability
to climate change impacts in Australia and New Zealand. Degree of confidence
that tabulated impacts will occur is indicated by a letter in the second
column (VH = very high, H = high, M = medium, L = low, VL = very low). These
confidence levels, and the assessments of vulnerability and adaptability,
are based on information reviewed in this chapter and assume continuation
of present population and investment growth patterns.